Vegetation cutting tool and method of manufacture

ABSTRACT

A hedge trimming tool having a fixed elongated blade mounted to the power head of the tool and a cutting blade mounted over the fixed blade and reciprocating relative to the fixed blade in the direction of the lengthwise axis. A leading side of the fixed blade has projecting fingers or teeth and the overlying portion of the cutting blade has projecting teeth that reciprocate across the openings between the fingers. The reciprocating teeth have sides configured in a complex curve forming an hour glass planar profile and an inverted U-shaped cross section. The U-shaped cross section is provideed by curving the sides of the teeth downwardly whereby the teeth sides are angularly projected through the plane defined by the bottom surface of the blade. The cutting edges along the sides are formed by grinding faces through the portions of the teeth projected below the bottom surface of the blade. The faces are formed in a single pass of the grinding implement with the faces parallel to the bottom surface of the blade.

This is a division of application for U.S. Patent, Ser. No. 07/546,428,filed June 29, 1990 and now U.S. Pat. No. 5,093,999.

FIELD OF THE INVENTION

This invention relates to vegetation cutting tools, having reciprocatingteeth such as used for trimming hedges, and more particularly it relatesto a cutting blade of the tool having teeth that are configured foreffective cutting and easy manufacture.

BACKGROUND OF THE INVENTION

Hedge trimming tools are required to cut vegetation ranging from smalllimbs, e.g. three-eighth inch diameter, down to the size of leaf stems.The conventional hedge trimming tool to which this invention is directedincludes an elongated fixed blade with forwardly projected teeth and anoverlying cutting blade reciprocally mounted to the fixed blade. Cuttingteeth carried by the overlying cutting blade are projected over theteeth of the fixed blade and reciprocate back and forth across thespacing between the fixed blade teeth. The tool is directed into oralong the hedge and as vegetation enters the space between the fixedblade teeth, it is severed by the reciprocating teeth.

Forming the teeth of the overlying cutting blade is a primaryconsideration in the manufacture of a hedge trimming tool. Heretoforethe teeth were produced in what can essentially be considered as atwo-step operation. First, holes or openings were made, e.g. by acircular punch driven through the blade thickness at the leading edge ofthe blade. The holes are formed so as to overlap the leading edgeresulting in a scalloped configuration having hour glass configuredteeth separated by C-shaped openings.

In the second step of the prior manufacturing process, a frusto conicalsharpening tool, rotated on its axis, is projected down into theC-shaped openings to bevel or flare outwardly the blade thickness fromthe bottom surface to the top surface of the blade. This creates cuttingedges along the concave curved sides of the hour glass configured teethat the bottom surface of the blade. The blade is laid with the bottomsurface flat on the fixed blade so that the cutting edges slide over thefixed blade fingers in a scissors-like slicing action.

The concern of this manner of forming the teeth is in the substantialrelative cost of forming the cutting edges, i.e. the step of projectinga rotating frusto conical sharpening tool into the C-shaped openings tobevel the blade thickness and thereby form the cutting edges.

THE PRESENT INVENTION

The present invention does away with the conventional practice offorming the cutting edges with a rotating frusto conical sharpeningtool. In the preferred embodiment, the same first step is performed tocreate the hour glass configured teeth separated by C-shaped openings inthe leading edges of the blade. The teeth (which are unfinished in thisstage of operation) are then curled or curved downwardly on both sideedges. This curling operation results in the top surface of the teethbeing angularly projected through the plane defined by the bottomsurface of the blade. A machining tool is directed along the bottomsurface of the blade and in a single machining operation grinds facesthrough the thickness of the downwardly projected sides of the teeth.The faces form acute angles with the top surfaces of the blade whichbecome the cutting edges.

Whereas in the present invention two operations are required to producethe desired cutting edges they are accomplished in but a fraction of thetime previously required by the process of sharpening with the frustoconical sharpening tool. Furthermore, it is desirable to offset theforces of the cutting edges below the bottom surface of the blade. Thisreduces the surface-to-surface contact between the blades which in turnreduces friction. Also, the configuration offers the potential of easyresharpening.

These and other benefits will be apparent upon reference to thefollowing detailed description and drawings referred to therein.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view illustrating a hedge trimming tool in accordancewith the present invention;

FIG. 2 is an enlarged section view taken on view line 2--2 of FIG. 1;

FIG. 3 is a partial side view as taken on view line 3--3 of FIG. 2;

FIG. 4 is an enlarged perspective view of a section of the cutting bladeof the tool illustrated in FIGS. 1-4 and FIGS. 4a and 4b are provided toillustrate and assist explanation of the manner of forming the complexlycurved cutting edge illustrated perspectively in FIG. 4;

FIGS. 5a and 5b illustrate the hole forming step used in producing thecutting blade of FIG. 4;

FIGS. 6a, 6b and 6c illustrate the edge curling step in producing thecutting blade of FIG. 4; and

FIG. 7 illustrates the edge sharpening step in producing the cuttingblade of FIG. 4.

Reference is made to FIGS. 1-3. Illustrated in FIG. 1 is a hedgetrimming tool 10 that is adapted to be mounted to a power head (notshown). A bottom blade 12 of the tool -0 is fixedly mounted to the powerhead. A cutting blade 14 overlies the fixed blade 12 and is coupled tothe power head's output shaft as represented by coupling arm 16. A flatholding bar 18 is secured to the fixed blade 12 by rivets 20. Slots 22in the cutting blade 14 allow the cutting blade 14 to reciprocaterelative to the fixed blade 12 and holding bar 18 as indicated by arrows24. Reciprocation of cutting blade 14 is provided by the output shaft ofthe power head coupled to the cutting blade 14 (indicated in the drawingas coupling 16).

The hedge trimming tool 10 is operated to direct the tool in a sweepingaction in either of the directions indicated by arrows 26 and 28.Whereas the tool can be constructed to function in one or the other ofthe directions 26; 28, typically for convenience and versatility thetool is designed to function in both directions as illustrated.Hereafter when reference is made to the leading edge of the tool or itscomponents, i.e. the leading edge of fixed blade 12 or reciprocatingblade 14, it will be understood that the term has reference to thedirection of operation and includes one or both leading edges determinedby the arrows 26, 28.

As can be seen in FIG. 1, the fixed bottom blade 12 is scalloped alongits leading edge to produce forwardly directed fingers or teeth 30.These teeth are spaced apart a distance to receive therebetween themaximum thickness of branches of a hedge to be trimmed, e.g.three-eighth inch. The reciprocating blade 14 is scalloped along itsleading edge in a manner to produce cutting teeth 32 (described indetail hereafter). These teeth 32 reciprocate between a retractedposition with the teeth 32 overlying the teeth 30 (shown in solidlines), and in a closed position with the teeth 32 positioned betweenthe teeth 30 (as illustrated in dash lines designated 32' the upperright end of FIG. 1). It will be understood that branches (less thanthree-eighth inch diameter), twigs, leaves and the like slide into thespaces between teeth 30 and then into the opening between the cuttingteeth 32, (i.e. with the cutting teeth reciprocated to the retractedposition). The teeth 32 close across the opening (position 32') with thetips 33 of the cutting teeth first hooking and drawing the materialsinto the opening. Continued movement of the teeth 32 across the opening,in cooperation with the opposed stationary teeth 30, slices through andsevers the material. Several cycles of reciprocation may be required tosever the larger branches. However, the reciprocation is very rapid andthe operator "feel" is u interrupted.

All of the above written description is as applicable to prior hedgetrimming tools as it is to the illustrated tool of the presentinvention. The improvement provided by this invention is principallyembodied in the production of the teeth of the reciprocating cuttingblade and to a lesser degree, the operational benefit resulting fromreduced friction.

The teeth 32 of cutting blade 14 are formed out of complex curves whichcan best be seen from the perspective view of FIG. 4. Consider first theshape of the tooth when viewed from the top down as indicated by viewline 34 in FIG. 4 and as seen in the plan view of FIG. 1. The teeth 32of the blade 14 as shown in FIG. 1 at the upper left end have cuttingedges 44 that generate a top view profile of the teeth that isrelatively wide at the inner end 66 and outer tip 33 and relativelynarrow across the middle to produce the hour glass shape.

Referring now to FIGS. 4 and 4a, the teeth viewed from the end asindicated by view line 36, take on the shape of an inverted U. This isthe result of the sides of the cutting teeth being curved downwardly.The operation that forms this U shape curve is illustrated in FIG. 6c.The teeth are bowed, i.e. the teeth sides are curved downward so thatthe full blade thickness is projected angularly downwardly through theplane that is defined by the bottom surface 38 of the blade. (See FIG.6c at 48e.)

With reference to FIGS. 4a and 7, because the top surfaces 40 of theteeth segments are projected at an angle to the planar body of theblade, the depending sides of the teeth can be ground off parallel tobottom surface 38 (arrow 39 of FIG. 7) to form bottom teeth faces 42.The included acute angle α between faces 42 and top surface 40 in FIG.4a produces the cutting edge 44.

The advantages are primarily advantages in the production of the blade,but structural advantages are achieved as well. Note that the faces 42are slightly below bottom surface 38 of the blade. These faces 42 arethe only surfaces contacting and sliding on the top surface of fixedblade 12. The total contact surface is thereby a fraction of the contactsurface which would occur if the full bottom surface of the cuttingblade were to ride on the fixed blade 12 (as in prior hedge trimmingtools) and the frictional resistance to the reciprocating action of theblade 14 is significantly reduced

A further advantage that is conceived for this tooth configuration isthat the cutting edge 44 can be resharpened. See FIG. 4b wherein thecutting edge 44 is shown rounded as when worn. A resharpening mediaapplied against the faces 42 will result in the partial removal of thefaces 42 as indicated by dash lines 46 to generate a resharpened cuttingedge at the location of the reduced faces 42 as indicated at 44'. Thissharpening media can be a tool applied against the blade bottomfollowing disassembly of the blade from the fixed blade, or it can be anaggregate strip or even a slurry of aggregate that is inserted betweenthe blades. The tool is operated to reciprocate the blades for automaticor self sharpening.

As previously indicated, the primary benefit of the tooth configurationof the invention is in the simplified production of the blade. The stepsof production are illustrated in FIGS. 5-7.

FIGS. 5a and 5b schematically illustrate the traditional first stepwherein a die punch 46 having circular die cutters 47 punches circularholes 48 along both side edges 52 of a metal strip 50. (The metal stripwas previously cut to size, e.g. 0.070×1.69×24 inches, from a roll ofmetal sheet material, e.g. 24 inches wide and 0.070 inches thick andmany feet long.) The die punch 46 overlaps the edges 52 as indicated bythe dash lines 54 in FIG. 5a to form an open sided C-shaped opening 48.(As explained previously, in prior production processes, it is at thispoint that a frusto conical sharpening tool would be forced down througheach hole or opening 48 to bevel the thickness of the strip upwardly andoutwardly to form the sharpened edge coplanar to the bottom surface 38of the strips.)

The next step, which is a deviation from the prior processes and isunique to this invention, is the step of upsetting, curving or curlingthe metal at the sides of the teeth, illustrated in FIGS. 6a-6c. FIG. 6cis a cross section as will be apparent from noting the view lines ofFIGS. 6b and 6a. As will be most apparent from FIG. 6c, anvils 56 arepositioned under the metal strip 58 between the holes 48. A forming tool60 includes configured plungers 62. The plungers 62 are forced downthrough the openings 48 as illustrated in FIG. 6c to curl or curve theside edges of opening 48 around the anvil 56. It is important to notethat this forming step results in the hole edge 48e being forced into aposition that is below the planar bottom surface 38 of the body 50.

FIG. 7 illustrates the sharpening step which converts strip 50 to blade14 and produces the configured cutting teeth 32. A sharpening tool 6 issimply directed along the bottom of the blade in a direction 39,parallel to and spaced slightly below the bottom surface 38 asillustrated. Those skilled in the art will be aware of the manydifferent forms that tool 64 can take and the rotating cylindricalsharpening tool 64 of FIG. 7 is merely a schematic illustration of suchtools in general. (In actual practice, the blade is inverted and laid onits top on a work surface and a sharpening tool is passed over the topof the blade bottom 38 to sharpen the teeth.) The movement of thesharpening tool 64 across the blade bottom projects through the teethsides resulting in the formation of faces 42 and hence cutting edges 44.This final step of course converts the intermediate strip segments orportions 58 into cutting teeth 32.

The bar 18, cutting blade 14 and fixed bar 12 are then assembled intothe tool of FIGS. 1-3. As shown in FIG. 2, the rivet 20 is provided withan enlarged diameter center section 64 that spaces the bar 18 from blade12 to provide free sliding of the cutting blade 14. The faces 42 of theteeth 32 ride on the top surface of the fixed blade teeth 30. Theinnermost portion of the edge 44 is curved inwardly (as indicated at 66in FIG. 1) to a greater extent than tip 33 at the outer end of theteeth. The inner curve at 66 functions as a cam surface to maintain thecutting teeth at a level above the top surface of the fingers andinsures that the teeth 32 will not project into the spacing between andcatch on teeth 30.

As seen in FIG. 1, sliding of the reciprocating blade 14 is permitted bythe provision of slots 22 which are parallel to the direction ofreciprocating action indicated by arrow 24. It will be appreciated,however, that the two blades 12 and 14 can be reversed whereby cuttingblade 14 is fixed to the power head and blade 12 is reciprocated or, asa further alternative, both blades can be reciprocated but in oppositedirections.

Those skilled in the art will conceive of other, variations andmodifications without departing from this invention which is defined inthe accompanying claims appended hereto.

We claim:
 1. A process for forming a cutting blade for a vegetationcutting tool that comprises:forming open-sided openings in an edge of aplanar metal strip, said openings spaced close together and the metalmaterial between the openings forming unfinished cutting teeth, curvingthe sides of the unfinished cutting teeth downwardly whereby portions ofthe sides project angularly and downwardly through the plane of thebottom surface of the blade, and grinding faces through the portions ofthe teeth sides extended below the bottom surface of the blade, saidfaces being parallel to said bottom surface of the blade.
 2. A processas defined in claim 1 wherein the cutting teeth have concavely curvedsides curved in the plane of the metal strip and thereby forming aplanar profile that is hour glass configured.
 3. A process as defined inclaim 2 wherein the open-sided openings are formed in die stampingoperation and the sides of the teeth are downwardly curved bypositioning a forming anvil at the bottom of the unfinished teeth andforcing a configured plunger down through the openings to curve theteeth sides around the forming anvil.
 4. A process as defined in claim 3wherein the faces are formed by the pass of a sharpening tool directedalong a plane parallel to and spaced from the bottom surface of theblade.